According to the above-described solenoid-operated valve for a thermally insulated piping, a solenoid coil is disposed outside a heat-insulating layer which surrounds flow passages in the form of a pipe, and inside the heat-insulating layer, there are provided a movable core and a valve member operable to open or shut the flow passage in response to a reciprocating movement of the movable core. Then, the valve member disposed inside the heat-insulating layer may be opened or shut in association with a magnetizing/demagnetizing action of the solenoid coil, while restricting heat conduction from the inside to the outside of the heat-insulating layer. According to the conventional art, a magnetic circuit is comprised solely of the movable core disposed inside the heat-insulating layer to be movable in response to a magnetizing/demagnetizing action of the solenoid coil (for example, see Japanese laid-open patent gazette Sho. 61-252984).
For this reason, the magnetic resistance between the solenoid coil and the core is large. Then, in order to allow the movement of the movable core associated with magnetization of the solenoid core to take place in a reliable manner, it is necessary to increase the magnetic flux density by increasing either the number of turns of the coil or the electric current, thus resulting in problem of high production costs or high running costs.
In order to solve this problem, it is conceivable, for instance, to provide the movable core with a sufficient length in the longitudinal direction of the flow passage, thereby to minimize the magnetic resistance between the solenoid coil and the movable core. In this case, however, as the movable core is enlarged, the load needed for its movement is increased as well. As a result, just like the aforedescribed conventional art, for the reliability of movement of the movable core, it becomes again necessary to intensify the magnetic flux density of the solenoid coil by increasing the number of turns or the value of electric current to be applied thereto.
The present invention attends to the above-described state of the art, and an object of the invention is to provide a solenoid-operated valve for a thermally insulated piping and its attachment construction, which allow reduction in the production costs and running costs through ingenious arrangement of an interior construction of the heat-insulating layer.